IntroductionOverexpression of the oxygen-responsive transcription factor hypoxia-inducible factor 1α (HIF-1α) correlates with poor prognosis in breast cancer patients. The mouse mammary tumor virus polyoma virus middle T (MMTV-PyMT) mouse is a widely utilized preclinical mouse model that resembles human luminal breast cancer and is highly metastatic. Prior studies in which the PyMT model was used demonstrated that HIF-1α is essential to promoting carcinoma onset and lung metastasis, although no differences in primary tumor end point size were observed. Using a refined model system, we investigated whether HIF-1α is directly implicated in the regulation of tumor-initiating cells (TICs) in breast cancer.MethodsMammary tumor epithelial cells were created from MMTV-PyMT mice harboring conditional alleles of Hif1a, followed by transduction ex vivo with either adenovirus β-galactosidase or adenovirus Cre to generate wild-type (WT) and HIF-1α-null (KO) cells, respectively. The impact of HIF-1α deletion on tumor-initiating potential was investigated using tumorsphere assays, limiting dilution transplantation and gene expression analysis.ResultsEfficient deletion of HIF-1α reduced primary tumor growth and suppressed lung metastases, prolonging survival. Loss of HIF-1α led to reduced expression of markers of the basal lineage (K5/K14) in cells and tumors and of multiple genes involved in the epithelial-to-mesenchymal transition. HIF-1α also enhanced tumorsphere formation at normoxia and hypoxia. Decreased expression of several genes in the Notch pathway as well as Vegf and Prominin-1 (CD133)was observed in response to Hif1a deletion. Immunohistochemistry confirmed that CD133 expression was reduced in KO cells and in tumorspheres. Tumorsphere formation was enhanced in CD133hi versus CD133neg cells sorted from PyMT tumors. Limiting dilution transplantation of WT and KO tumor cells into immunocompetent recipients revealed > 30-fold enrichment of TICs in WT cells.ConclusionThese results demonstrate that HIF-1α plays a key role in promoting primary mammary tumor growth and metastasis, in part through regulation of TICs. HIF-1α regulates expression of several members of the Notch pathway, CD133 and markers of the basal lineage in mammary tumors. Our results suggest that CD133, which has not been profiled extensively in breast cancer, may be a useful marker of TICs in the PyMT mouse model. These data reveal for the first time that HIF-1α directly regulates breast TIC activity in vivo.

c Impairment of astrocytic glutamate transporter (GLT-1; EAAT2) function is associated with multiple neurodegenerative diseases, including Parkinson's disease (PD) and manganism, the latter being induced by chronic exposure to high levels of manganese (Mn). Mn decreases EAAT2 promoter activity and mRNA and protein levels, but the molecular mechanism of Mn-induced EAAT2 repression at the transcriptional level has yet to be elucidated. We reveal that transcription factor Yin Yang 1 (YY1) is critical in repressing EAAT2 and mediates the effects of negative regulators, such as Mn and tumor necrosis factor alpha (TNF-␣), on EAAT2. YY1 overexpression in astrocytes reduced EAAT2 promoter activity, while YY1 knockdown or mutation of the YY1 consensus site of the EAAT2 promoter increased its promoter activity and attenuated the Mn-induced repression of EAAT2. Mn increased YY1 promoter activity and mRNA and protein levels via NF-B activation. This led to increased YY1 binding to the EAAT2 promoter region. Epigenetically, histone deacetylase (HDAC) classes I and II served as corepressors of YY1, and, accordingly, HDAC inhibitors increased EAAT2 promoter activity and reversed the Mn-induced repression of EAAT2 promoter activity. Taken together, our findings suggest that YY1, with HDACs as corepressors, is a critical negative transcriptional regulator of EAAT2 and mediates Mn-induced EAAT2 repression.

Background: Tamoxifen (TX), a selective estrogen receptor modulator, enhances glutamate transporter (GLT-1) expression in astrocytes. Results: TX up-regulated GLT-1 expression via the CREB and NF-B pathways. Conclusion: TX enhanced GLT-1 expression at the transcriptional level. Significance: Understanding the mechanisms of TX action on GLT-1 will contribute to the development of neuroprotectants against excitotoxicity.

Background:The mechanism for transcriptional regulation of EAAT1 remains to be elucidated. Results: EGF-activated NF-B is a positive regulator of EAAT1, whereas manganese-activated YY1, with HDACs acting as co-repressors, is a negative regulator. Conclusion: NF-B and YY1 are two critical transcriptional regulators of EAAT1. Significance: Identifying the molecular targets of EAAT1 regulation is crucial to develop therapeutics against neurological disorders associated with impairment of EAAT1.